The present invention relates to apparatus for collecting a liquid sample, and in particular apparatus for collecting a sample of body fluid, for use in diagnosis.
Currently available apparatus used to collect small quantities of a liquid sample, such as a drop of blood from a finger prick, generally comprises a capillary tube of liquid-impervious material (such as plastic or glass), having a longitudinally extending hollow bore which is open at both ends. The internal diameter of the bore is typically approximately 0.1 to 3 mm and the length of the bore is typically about 50 mm. Such capillary tubes can take up liquid samples by capillary action. The sample is collected until the sample reaches a desired level in the bore (such as that indicated by markings or calibrations on the tube), or until the bore is completely filled, thus giving a known volume of sample. The liquid sample is subsequently transferred to an absorbent medium by contact of one of the open ends of the tubes with such an absorbent medium, for analysis.
One of the main problems with currently available capillary tubes is undesired entry of air into the bore if the uptake of liquid is deliberately or accidentally interrupted. This can cause an air lock in the bore, which hinders accurate collection of a predetermined volume of sample, and may lead to the collected sample flowing back down the tube and then dripping from the bottom end thereof. Furthermore, when collecting a sample of blood from a finger prick, it might be necessary to place the capillary tube down and squeeze out an extra drop of blood. It would be an advantage, therefore, if the uptake of a liquid sample by a capillary tube could be interrupted without the associated problems caused by entry of air into the bore.
It is an object of the present invention to provide an improved apparatus for collection of a liquid sample, which alleviates the problems associated with the prior art.
It is another object of the present invention to provide a method for analyzing a liquid sample using an improved capillary tube.
It is a further object of the present invention to provide a diagnostic kit for analyzing a liquid sample, again including an improved capillary tube.
The present invention provides apparatus for collection of a liquid sample, the apparatus comprising a tube having a hollow bore extending longitudinally between a first open end and a second open end, the second end being longitudinally spaced from the first end. The first end comprises a capillary opening for uptake of the liquid sample by capillary action, the capillary opening having a first axis and a second axis substantially perpendicular thereto. The first axis has a length greater than the internal diameter of the bore, and the second axis has a length less than the internal diameter of the bore.
The capillary opening is typically narrower than the internal diameter of the bore. This advantageously reduces the risk of entry of air into the bore when uptake of the sample is deliberately or accidentally interrupted. The likelihood of an airlock occurring in the bore may thus be minimized according to the invention.
The capillary opening may be provided by a flattened substantially rectangular pinched end of the tube. A tube with a flattened substantially rectangular pinched end is generally relatively cheap and easy to manufacture.
It is a preferred feature of the invention that the capillary opening has at least one side of greater length than the remaining sides. The side of greater length generally provides a flat sided extension which typically aids collection of a liquid sample. For example, it may be easier to apply a drop of blood from a finger prick to a flat sided extension than to a narrow opening of a tube.
The side of greater length preferably has at least one longitudinal groove which extends into the capillary opening. The grooves desirably draw the liquid sample from the point of collection towards the capillary opening of the bore.
In one embodiment of the present invention, the capillary opening includes a plurality of channels. Each of the plurality of channels preferably extends substantially along the capillary opening; more preferably they extend into the bore of the tube. The channels may be non-enclosed grooves, which typically channel the liquid sample into the bore, or alternately each channel may be a separate enclosed tubular conduit.
The amount of liquid sample a capillary tube can be charged with according to the invention depends on various factors, including the physical chemistry of the sample, the material used to make the tube, and the angle of contact of the capillary opening with the sample.
The aforementioned plurality of channels may advantageously enable faster charging of the liquid sample as each channel provides an independent capillary action.
It is a preferred feature of the present invention that at least part of the tube is optically transparent, enabling viewing of the collected liquid sample. The tube may be made of suitable extrudable plastics, such as polyethylene, polypropylene, or the like.
In a further embodiment, the tube has at least one calibration, such that an accurate volume of liquid sample can be collected. The bore may also be of predetermined length and internal diameter, such that when the bore is filled with liquid sample, a known volume is contained within the bore.
In a further embodiment of the present invention, the apparatus includes an outer barrel arranged to substantially surround and receive the tube. The outer barrel is typically hand holdable to aid collection of the liquid sample. The outer barrel is preferably provided with at least one transparent window such that at least part of the contents of the tube can be viewed. It may be appropriate to have at least one calibration on the transparent window, or for the window to be positioned such that at least one calibration on the tube can be viewed through the window.
It may sometimes be desirable to include at least one preservative for the liquid sample, the preservative being arranged to be received in the bore. For example the internal surface of the bore may be coated with a suitable chemical which prevents deterioration of the liquid sample through microbial contamination or clotting.
The present invention further provides a method for analyzing a liquid sample, which method comprises the following steps:
providing at least one tube having a hollow bore extending longitudinally between a first open end and a second open end, the second end being longitudinally spaced from the first end, the first end comprising a capillary opening, the capillary opening having a first axis and a second axis substantially perpendicular thereto, the first axis having a length greater than the internal diameter of the bore, and the second axis having a length less than the internal diameter of the bore;
(1) contacting the capillary opening with the liquid sample, such that the sample is taken up into the tube by capillary action;
(2) transferring the collected sample to a receiving member; and
(3) analyzing the sample on the receiving member. Suitable liquid samples for analysis include blood, tears, urine, saliva, sweat, intestinal secretions, and the like.
The receiving member, mentioned in step (c) above, may comprise an absorbent material. The liquid sample may be transferred to the absorbent material by contact between the absorbent material and at least one of the first and second open ends of the tube. The second open end of the tube may be arranged to be permanently in contact with the absorbent material.
Furthermore it is sometimes desirable to collect a predetermined volume of the liquid sample which may then be transferred to the receiving member.
The sample may be analyzed using any of a number of methods known in the art, for example by an immunoassay or enzyme linked immunosorbent assay (ELISA). Alternately, the receiving member may be a microscope slide, and the sample may be analyzed using a microscope. The sample on the microscope slide may be stained using a differential stain, for example a gram stain, to typically stain target prokaryotic or eukaryotic cells. Alternately, a microscope may be used to count the number of specific cells present in a set volume of liquid sample transferred to a microscope slide.
The tube may be of any suitable longitudinal shape, such as arcuate or otherwise curved along the length, or it may have a substantially linear axis. A curved tube may advantageously enable collection of the liquid sample at the first open end of the tube with simultaneous dispensing of the sample from the second open end of the tube. The sample may be dispensed from the second open end directly onto the receiving member.
The present invention further provides a diagnostic kit for analyzing a liquid sample, which comprises at least one apparatus as described above and a reagent for reacting with a predetermined component of the liquid sample. For example, a diagnostic kit may include a reagent to test the presence of allergen specific IgE in a drop of blood.
The diagnostic kit preferably further includes a receiving member for receiving the liquid sample from the apparatus. The receiving member may be as hereinbefore described. At least one preservative for the liquid sample is preferably included in the diagnostic kit. The preservative may be as described above.